Update...

The carbon monoxide detector went off because our HVAC damper had shut and the exhaust was blowing back into the house. The repairman cleaned out gobs of soot and all is working well again.

He gave us some good advice that I'd like to pass along:

1) Have a detector in the room with your unit.
2) Have a detector outside this room as a backup.
3) Calm your nerves by testing your detector. Take it outside to the vent where the carbon monoxide exits and place it underneath the vent. It should immediately go off. Then place it back inside. You will now know for certain that the detector is working properly.
4) Have a battery operated and a plug in detector. (this will eliminate the "eh, it's just the battery" response that I had.)
5) Change the batteries along with your smoke alarms with daylight savings. This particular admonition has always irritated me, b/c as a minimalist, I think that you are just wasting perfectly good batteries. Just put those semi-used batteries in their own Ziploc and label them "post-detector". They can be finished out in a camera, flashlight, etc.

....tune in for more exciting adventures from the "Beckett diaries".....